I found this PDF G2P_FSD-Interlocks_Meeting_Minutes_29Nov2011.pdf that states on bullet 6:
"Compton Electron Detector – not used for the experiment – permanently masked – leave the text on the screen"
I've asked MCC to double check that this FSD was not masked previously.
Figure 1
G2P_FSD-Interlocks_Meeting_Minutes_29Nov2011.pdf